1. Field of the Invention
The invention relates to apparatus for determining a d-c potential in metal-encapsulated high-voltage switching installations and equipments and, in particular, installations and equipments which comprise at least one conductor carrying the high voltage and supported within a grounded encapsulation via insulators.
2. Description of the Prior Art
In metal-encapsulated high-voltage switching installations and equipments of the above-type, the conductor intended to carry the high-voltage a-c current can be grounded, so that it is possible for repair and maintenance personnel to work on the installation without danger. More particularly, in VDE (Society of German Electrical Engineers) Specifications 0105 Part 1, procedures are described under Item 5, which must be taken to secure and ensure a voltage-free condition of the high-voltage conductor before work can begin on the installation. The absence of voltage is in general ensured by providing in the installation grounding switches which tie the conductor electrically to the surrounding metal-encapsulation. However, before a grounding switch is operated, it is desirable to ascertain whether there is a voltage on the high-voltage conductor so as to avoid exposing the grounding switch to an arc.
The presence of an a-c voltage on the conductor can be determined by means of an electrode which is arranged in an insulated manner between the conductor and the encapsulation and which delivers a signal if an a-c voltage is present. Such a simple electrode arrangement, however, does not detect a d-c voltage on the conductor. Such a voltage may be present between the conductor and the encapsulation if, after the a-c supply lines have been disconnected, the high-voltage switching installation still carries electric charge due to the unavoidable capacities, particularly of cables.
It is an object of the present invention to provide an arrangement for detecting the d-c voltage on the high-voltage conductor of the above-described metal-encapsulated high-voltage switching installations.